Search engines try to discover cloakers by using a number of techniques:
By visiting using an IP address which is not registered to their company.
By visiting using a non-spider user agent
By comparing caches from different sources that they own; i.e., from their main spider and from their page accelerator
By comparing caches from different sources that they don’t own; i.e., from their main spider and from some other company’s cache
By using an algorithmic process to identify likely candidates and using human editors to verify.
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